Test Distribution

It’s the distribution that $\overline{X}$ follows where the population is normal, ${\sigma }^2$ is unknown, and you only have a small sample at your disposal.

where $v=n-1$ (degrees of freedom)
standard score:

To find $t(\nu )$, you need to look it up in t-distribution probability tables. To do this, use $\nu =n-1$ and your level of confidence to find the critical region.

Sources: 1